Power usage is a primary concern for many consumer electronics devices. As a solution, many known devices are adapted to selectively operate certain circuitry so that battery resources are utilized as sparingly as possible. For example, a mobile phone may turn off camera circuitry while a user is on a call. To do so, the camera circuitry may be electrically isolated from the battery so it ceases to draw current from the battery.
This approach creates problems in the design of the integrated circuits (ICs) that operate electronic devices, because the selective turning on and off of circuits referenced to a power supply causes variations in a supply voltage. For most electrical circuits to operate properly, they must be referenced to a stable supply voltage.
Many solutions have been proposed for voltage regulators to stabilize a power supply voltage under varying load conditions. One known approach is a source follower (also known as a common-drain amplifier or voltage follower) such as an NMOS source follower. A classic NMOS source follower includes an N-Channel transistor (known as a pass transistor). A drain of the pass transistor is coupled to a load to supply power. The voltage across the load is fed back to a differential amplifier that supplies a control voltage at the gate of the pass transistor.
A source follower solution operates relatively well to stabilize a supply voltage for circuits that operate at frequencies such as 1 Mhz and above. However, a source follower typically operates poorly for circuits operating at lower frequencies such as below 100 kHz. Because many integrated circuits require a regulated supply voltage at all frequency ranges, a source follower may be undesirable in many applications.
In addition, to effectively regulate a power supply, a source follower typically requires a relatively large output capacitor to ensure enough charge is available to compensate for changes in the load powered by the regulator. Such a capacitor often takes up a large amount of space on an integrate circuit or must be off-chip connected to a capacitor in an IC package.
Other approaches to power regulation, such as discussed in U.S. Pat. No. 6,653,891 to Hazucha et al., incorporate some form of additional feedback loop to improve upon an ability of a source follower voltage regulator to regulate voltage and current supplied to a load in light of varying load conditions. For example, U.S. Pat. No. 7,319,314 to Maheshwari et al. discloses the use of a dual difference amplifier stage feedback circuit and a voltage replicator to better stabilize a supply voltage. Similarly, U.S. Pat. No. 7,446,515 to Wang, U.S. Pat. No. 6,809,504 to Tang et al., U.S. Pat. No. 6,975,494 to Tang et al., U.S. Pat. No. 6,188,211 to Runcon-Mora et al., and U.S. Pat. No. 5,867,015 to Corsi et al. describe other various dual stage regulators. Still other approaches, such as U.S. Pat. Pub. No. 2009/0033298 to Kleveland, combine analog feedback circuitry with a digital controller and one or more sense circuits to provide additional feedback in light of varying load conditions.
A common drawback of the above-mentioned approaches is that each involves a relatively complex configuration of transistors and other circuit components, which not only requires significant space in an integrated circuit, but also increases design and IC implementation costs. And, for many known solutions, additional space on an IC, a circuit board, or in an IC package is required due to a need for a relatively large capacitor. Further, although the above-mentioned regulators may provide improved stability at a range of frequencies, they do so at the cost of relatively large current draw of the regulator itself, which is inefficient for purposes of preserving battery life.
Thus, a need exists in IC technology to provide an improved variable load voltage regulator for integrated circuits that has improved stability at both low and high frequencies of circuit operation. Also, a need exists to provide such a voltage regulator that does not require a large capacitor. Furthermore, a need exists for a simple, inexpensive, and easy to design voltage regulator for variable load integrated circuits.